We propose to 1) assess the rate of exchange of heme from serum albumin to hemopexin in vitro, 2) extend our studies on the interaction in vitro of naturally occurring and synthetic porphyrins with hemopexin to increase our knowledge of the porphyrin binding site of hemopexin, and 3) investigate the in vivo effect of porphyrinogenic agents and prophyria on the metabolism of hemopexin in experimental animals and man, respectively. BIBLIOGRAPHIC REFERENCES: Porphyrin binding proteins in serum. U. Muller-Eberhard and W.T. Morgan, Ann. N.Y. Acad. Sci. 244:624-650, 1975. Bilirubin production from erythroid sources. U. Muller-Eberhard and E.F. Johnson, JAUNDICE (Plenum Press, New York) pp. 69-83, 1975.